This proposal examines the relationship between hypoxic neuronal damage and glutamate (GLU) neurotoxicity. An hypoxic-ischemic episode, as might occur focally during stroke or cerebral hemorrhage or globally during cardiac arrest, results in the accumulation of external GLU and neurodegeneration. It is unknown if hypoxia-induced neuronal lysis liberates excessive GLU or if metabolically compromised, intact neurons release GLU which then exerts further toxic effects. A detailed hypothesis is presented to explain the elevations of intracellular free calcium ion (Cal) and accumulation of endogenous GLU following metabolic compromise. In this model, eventual toxicity results from the enhanced deleterious effects GLU rather than the initial hypoxia. Combinations of hypoxic insult and exogenously applied GLU are expected to produce additive, or supraadditive, effects in this scheme. Experiments are proposed to measure survival of dissociated, hippocampal neurons maintained in a tissue culture environment after individual and combined exposure to excitatory amino acids (EAA), oxygen deprivation, and sodium cyanide (NaCN) as a model of "chemical hypoxia". Additional measurements will be made of resting and altered levels of Cal and intracellular pH (pH1) to determine involvement of these ions in the response to toxic insult and in the signal pathway leading to neuronal death. Methods are proposed for documenting the release of endogenous glutamate after hypoxic insult. Surviving neurons will be examined for their physiological responses to EAA and for the presence or absence of specific cytoplasmic calcium-binding proteins to identify cellular processes possibly conferring resistance to toxic insults.